Okay, maybe not the best upgrade... but definitely up there. One of you guys suggested I swap the window while the body was stripped for paint - I owe you a beer(s)! Now that the bed has some steel on it and the exhaust is finished (and dumps to side/behind the rear wheel), I can finally open that window without sucking in exhaust. I was just driving - windows and wing windows open - but still not getting a lot of air... realized I'd closed the back window... slid it open... Wow. It really does allow a LOT more air to move through the cab.